In recent years, in order to handle various large-volume data in various government, corporate and university institutions and other types of institutions, data has been managed using comparatively large-scale storage apparatuses. A large-scale storage apparatus of this kind is configured having a plurality of storage devices (hard disk drives and so on, for example) arranged in an array. For example, one RAID (Redundant Arrays of Independent Disks) group is configured from one or more hard disk drives, and one or more logical volumes are defined in a physical storage area provided by one RAID group. Furthermore, the logical volumes are provided to a host apparatus. The host apparatus is able to perform data writing and reading by transmitting predetermined commands to the logical volumes.
In order to handle the various large-volume data, a storage apparatus (hereinafter a storage apparatus will be referred to as a virtual storage apparatus), which provides a storage area of another storage apparatus to the host apparatus as part of its own storage area, is realized. For example, PTL1 discloses a technology which connects another storage apparatus (hereinafter the other storage apparatus will be described using the term external storage apparatus) to the virtual storage apparatus and provides virtual volumes to the host apparatus. By using actual volumes in the external storage apparatus (hereinafter the actual volumes are described using the term real volumes) as the storage area of the virtual volumes, the storage area of the external storage apparatus can be used as if this storage area were part of the storage area of the virtual storage apparatus.